Nonwoven fiber webs frequently consist of a random yet homogeneous agglomeration of long and short fibers, Long fibers are fibers of both natural and synthetic origin that are suitable for textiles. They are longer than 0.25 inches and generally range between 0.5 and 2.5 inches in length. Short fibers are suitable for paper-making and are generally less than about 0.25 inches long, such as wood pulp fibers or cotton linters. It is known in the art that strong nonwoven webs can be made by rapidly and reliably blending inexpensive short fibers with strong long fibers.
Nonwoven fabrics are less costly than woven or knitted material, yet are more or less comparable in physical properties, appearance, and weight. Thus, inexpensive nonwoven fabrics are available for a wide variety of products, including, hand towels, table napkins, sanitary napkins, hospital clothing, draperies, cosmetic pads, etc. These nonwoven webs can be particularly advantageous when formed as a layered or composite material having a varying area in horizontal cross-section at various vertical locations.
Methods and machines for making nonwoven fluff pulp pads and pre-shaped absorbent products are known, but do not provide for selective blending and layering of pulp, textile, and particulate materials. Conventional pocket-forming devices can process only one material, usually pulp, and cannot be readily modified to provide uniformly blended pads because of the complex geometry inherent in the use of hammer mills or disc mills and cylindrical product-forming surfaces. Typical of these conventional devices are machines available from Winkler & Dunnebier Maschenfabrik and Curt G. Joa, Inc. See, for example, U.S. Pat. Nos. 4,560,379 and 4,598,441 of Stemmler. [owned by W&D]. PCT Application No. WO 85/04366 of Johnson et al. is also of interest. Johnson teaches the use of fiber-receiving molds disposed on a continuously rotating drum selectively provided with a vacuum. Other foraminous drum arrangements having circumferential cavities are taught by U.S. Pat. No. 4,592,708 of Feist et al. and U.S. Pat. No. 3,518,726 of Banks.
An early method of making sanitary napkins is disclosed in U.S. Pat. No. 2,073,329 of Winter. Winter teaches that patches of loose cotton fibers may be blown down onto a gauze-like material at regular intervals in cooperation with a suction means. Then pads of absorbent material may be placed over the cotton patches, and the gauze folded and cut at regular intervals to make the napkins. The loose cotton fibers are directed to the surface of a moving wheel having spaced and screened suction inlets adapted to receive and condense the cotton fibers in uniform patches. The Winter process requires several time-consuming and independent steps, followed by the assembly of the composite structure from its component structures. It does not provide for a composite shaped and layered structure formed by blending one or more fibrous and/or particulate materials in an integral operation.
U.S. Pat. No. 2,949,646 of Clark is also representative of the prior art, and sets forth the problem of providing three-dimensionally shaped structures having sharply defined edges. Clark recites a prior art method wherein fibers are deposited continuously from an entraining air stream onto a continuously moving foraminous belt provided with suction. The belt is partially masked in order to provide deposition and condensation of fibers into a web having the desired shape. Clark notes that this method is disfavored because of the leakage of fibers from the masked to the unmasked regions of the belt, resulting in non-uniform layers. The prior use of pans to catch fibers deposited by gravity is mentioned by Clark, as is a method of cutting web to desired shapes, or separating webs using caul plates.
The improvement of the Clark invention over the prior art is a fiber depositing head whereby unblended web structures having contoured edges are made by entraining previously individualized fibers in a circular path within a circular housing, delivering uniform volumes of entrained fibers to a moving collecting wall through openings in a foraminous separating wall of the housing, and forming a continuous web from the delivered fibers over collecting or masking members on the collecting wall. A clean separation of the continuous web into individual mats is achieved by a trough arrangement on the collecting wall, which trough separates adjacent collecting members and prevents leakage of fibers onto the collecting members by trapping excess fibers. A means for separating the masked collecting members from the end-product is also described.
A number of absorbent articles, and methods and machines for making them, are disclosed in the patents of Kolbach, U.S. Pat. Nos. 3,846,871; 3,860,002; 3,973,291; and 4,016,628. The '002 and '628 patents relate to adhesively bonded composite structures having a medial portion of grater basis weight than flanking end and side portions. These structures are obtained by providing discrete zones of relatively high and low suction on a foraminous forming surface.
The '871 and '291 patents describe a moving pad forming assembly having spaced, three-dimensional fiber-receiving compartments separated by air-impermeable regions. Each compartment has the shape of the desired end-product and is provided with a foraminous lower surface and movable air-impermeable side walls. Individualized fibers are provided to the compartments, which in turn communicate with a fiber-entraining suction means. Selective masking of the suction means can be used to influence the density and weight of material collected within regions of each compartment, and different air-suspended fibers are deposited to different compartment sections at different, non-overlapping, times to achieve different weight and density zones within each compartment.
U.S. Pat. Nos. 3,939,240 and 4,005,957 to Savich disclose a method and an apparatus for forming fibrous pads. Savich teaches a continuously driven condenser roll having three-dimensional foraminous cavities about its periphery. Each cavity is provided with a vacuum and is brought into communication with a pad forming region that is supplied with air-suspended fibers. The fibers are deposited within the cavity and form a layer, after which each layer is removed from its cavity as a pad by another vacuum cooperating with a proximate downstream transfer conveyor. The opening into each cavity has a smaller surface area than the surface area within the cavity, so that the resulting pads are consolidated within the cavity, resulting in an increased basis weight, rather than an advantageously shaped and sharply defined composite web structure.
The prior art does not provide discrete composite nonwoven structures having predetermined shapes and consisting of layers and/or vertical zones comprising blends of long fibers, short fibers and/or particulate matter. A method and apparatus capable of providing these structures is unknown, and in particular the prior art methods do not teach a means of producing such structures in a single continuous operation.